Just an update: We are currently road testing our down pipe with high flow cat in combination with our catback. So far we have about 300-350 miles on the car and no check engine light even... Crossing our fingers at the moment that we may not need an ECU flash to trick the car with our high flow cat version.

The Catless downpipe will need ECU flash or another work around to get rid of the O2 sensor error.

Challenge Sport catback Exhaust with Challenge downpipe with High Flow Cat. The downpipe added a good amount of grunt down low and in the midrange without adding any additional noise at crusing speeds. The cold start is now a bit louder than before and the over all exhaust note is a bit deeper with a hint of turbo noise in it When the Ecu is put in sport mode, you also get a bit more burble and poping noise off throttle

Sounds great with the catted downpipe. Can't wait to get this. So no dash lights because it is a catted downpipe correct?

No CEL yet with the high flow cat downpipe with the 350 miles or so yet. I should be putting another 200+ miles on it this weekend and see if its still off. We're pretty shocked it hasnt popped up really.

No CEL yet with the high flow cat downpipe with the 350 miles or so yet. I should be putting another 200+ miles on it this weekend and see if its still off. We're pretty shocked it hasnt popped up really.

We're about 600+ miles into it. No CEL with the HFC downpipe so far. We'll likely release it with a notation that with the current ECU version it shouldnt trigger a o2 sensor code. We'll get the ECU map version from the dealer. BMW likes to update the maps sometimes but you can choose to not update them for example.

None of our exhausts are CARB exempt etc. We don't have smog tests in this area, so i cant say if it would pass by you with the HFC. It's a 200 cell unit. Most states now only require an OBD2 scan for a clean bill of health.